Please read what I’m going to say, because your seller experience can depend on understanding this (don’t take this as me being condescending, this is important to understand):

Amazon is a marketplace. So visualize it as a farmers market.
You want to sell bananas. So Amazon told you that you can stand in the corner where they are selling bananas.
Now, Amazon didn’t say what bananas you could sell. It didn’t say if they were Chiquitas or Dole. It just said that you could sell bananas.
So you go to the corner and set the stand to sell the bananas. But somebody else is already selling Chiquita, and that seller has a letter of authorization, straight from Mr. Chiquita, selling that they are the only ones who can sell Chiquita. In other words, you’re not authorized to sell Chiquita. Same thing happens at the Dole stand.

There are multiple things that can happen. If you spoke with Mrs. Dole or Mr Chiquita, and they wrote you a letter saying that you can sell their products, then the current sellers (begrudgingly) will have to give you a space on their stand (fight for the buybox). If you don’t have the express authorization by either Dole or Chiquita, not only will they not share their stands, they will tell Amazon (the marketplace) to kick you out. Amazon will do it, and will put a picture of your face in the entrance saying “banned for ever”

If you have another brand of Bananas, and you’re authorized to sell those, or if they are unbranded bananas, then you can sell them without interfering with Mr. Chiquita or Mrs. Dole.